The reset switch is either bad and needs to be replaced or the motor is on its way out. Roger
If your check valve is working right, and your unloader valve for the compressor works right, you should have no back pressure for the compressor and motor to overcome.All of what Rog said and I think it sounds like the Start windings are going out of the Motor. With no air in the tank it might not need the start windings like it would when you have some load on it from air in the tank. Just a thought.